Heretofore, a process has been known which comprises forming a latent image on a latent image carrier, developing the latent image with an insulating toner which has been electrically charged by friction with a carrier or a charging member or the like constituting a part of a developing apparatus, electrostatically transferring the toner image onto a medium such as recording paper, and then fixing the toner image on the medium. This process has been widely put into practical use.
This process is disadvantageous in that the frictional chargeability of the insulating toner is governed by the humidity of the atmosphere or the like, making it difficult to obtain a stable image. A process as disclosed in JP-A-49-4532 ( The term "JP-A" as used herein means an "unexamined published Japanese patent application"), which comprises developing a latent image with electric charge induced by an electrically-conductive toner by the action of electrostatic charge on a latent image carrier, is advantageous in that it is little subject to the effect of the humidity of the atmosphere, making it possible to obtain a stable image. However, this process is disadvantageous in that the toner image cannot be electrostatically transferred.
The above process which comprises electrostatic transferring and subsequent fixing is also disadvantageous in that it requires not only a transferring apparatus and a fixing apparatus but also a carrying apparatus for carrying recording paper from the transferring apparatus to the fixing apparatus. This adds to the number of the constituent elements of the recording apparatus, enlarging and complicating the structure of the recording apparatus.
In order to overcome the foregoing difficulties, a simultaneous pressure transfer and fixing process is proposed as disclosed in JP-W-57-501348 (the term "JP-W" as used herein means an "unexamined published international application"), and a simultaneous heat-assisted pressure transfer and fixing process is proposed as disclosed in JP-A-63-106681. These processes do not involve electrostatic transferring and are thus little subject to the effect of the humidity of the atmosphere, enabling development with an electrically-conductive toner. It is also known in the simultaneous pressure transfer and fixing process that it is effective to incorporate an aliphatic metal salt or other lubricants in the toner to prevent maltransferring as disclosed in JP-A-63-135980.
In order to effect the simultaneous transfer and fixing process at a lower pressure, a pressure-fixable microcapsule toner is useful as disclosed in JP-A-59-184385. It is further known that a polymer which stays liquid at a low glass transition temperature or a polymer solution, i.e., pressure-fixable microcapsule toner containing a liquid fixable material in its core as disclosed in JP-A-59-162562 and JP-A-58-145964 is preferably used to provide a higher fixing strength.
However, such a pressure-fixable microcapsule toner having a liquid core is disadvantageous in that part of the liquid core which has flown out from the capsules broken is attached to the latent image carrier at the simultaneous transfer and fixing process and left not thoroughly cleaned out, causing a so-called ghost phenomenon in which the toner is attached to that area at the subsequent development step. In order to inhibit this phenomenon, it is effective to incorporate an aliphatic metal salt or other lubricants in the toner. However, this approach is disadvantageous in that such an additive is separated from the toner while being used with a copying machine or printer, staining the interior of the copying machine or printer. In particular, such an additive which has been separated from the toner and attached to a developing roll enhances the electric resistance of the surface of the developing roll, inhibiting the electrostatic induction to the electrically-conductive toner and hence giving a deteriorated image quality. This approach is also disadvantageous in that the separation of such an additive from the toner causes a change in the resistance of the toner, making it impossible to provide a stable image.